Temperature compensation for direct current telemeters



F. R. SIAS 2,343,159

TEMPERATURE COMPENSATION FOR DIRECT CURRENT TELEMETERS Feb. 29, 1944.

Original Filed NOV. 21, 1942 Inventor: v Frederick RSias,

His Attorney.

Patented Feb. 29, i944 TEMPERATURE COMPENSATION FOR v DIRECT CURRENT TELEMETERS Frederick R. Sine,

Marblehead, Mesa, assignor to General Electric Company, a corporation of New York Original application November 21, 1942, Serial No.

Divided and this application Septem-' her 1, 1943, Serial No. 500.80

3 Claims. (Cl. 171-95) My invention relates to telemetering systems and receivers therefor as well as'ratio instruments and this application is a division of my aplication Serial No. 468,436, filed November 21, 1942.

It is an object 01' my invention to provide arrangements for compensating for the eil'ect of variations in temperature. either ambient temperature or self-heating eflects in the receivers of telemetering systems, particularly those employing transmitting units of the variable resistance .or potentiometer type, and acting by producing variations in the relative receiver circuits.

Other and further objects and advantages will become due as the description proceeds.

current flow in the two A form 01' direct current telemetering system now known to those skilledin the art employs what, may be called a ratio type receiver in con- Junction with a transmitter in the form of a resistor or potentiometer having the end terminals or the resistor connected in series with the two ratio circuits of the receiver and having a sliding brush connected to one terminal of 9.. current source, theother terminal of which is connected to a Junction terminal 01' the two circuits oi the receiver. The receiver circuit comprises a pair of coils wound with relatively 'ilne copper wire or other metallic wire having an appreciable positive temperature coemcient of resistance. The potentiometer or transmitter resistor, on the other hand, is ordinarily composed of resistance wire comprising'a which has a relatively low or zero temperature coeflicient of resistance. In consequence, whenever the transmitter brush is away from the'position of balanced currents in the receiver coils, the temperature eflects in the two receiver coils are unequal because the circuits contain diil'erent proportions of resistance elements having ap0sitive temperature coeflicient of resistance and hav- 1%; a substantially zero temperature coefilcient o resistance.

The receiver coil in which the greater current flows produces the greater effect on the movable element of the receiver and consequently ordinarily hasa predominant efiect on the determination 01' the angular position of the movable element of the receiver. However, this coil is also the one which is more greatly aflected by variareason that it for the reason proportion 01 positive temperature coeiil- A rise in temperature theretions in temperature both for the is more greatly heated electrically or that its circuit contains a greater resistance having a cient of resistance.

material such as constantin fore has the eflect of weakening the receiver coil carrying the greater current. This results in the movable element of the receiver tending to defiect toward the mid position with the rise in temperature and to deflect away from the mid position with a fall in temperature.

My invention has for its object the elimination or minimizing of this eflfect. In my parent application I have disclosed and claimed a compensating arrangement employing a stationary block oi metal which has a negative temperature coeflicient of permeability arranged to attract the movable element toward the mid position at relativelylow temperatures and with a diminishing effect at higher temperatures, in order to compensate the opposite effect which results from temperature eflect on the receiver coils. In this divisional application this result is accomplished electrically.

A better understanding of the invention will be afforded by the following detailed description considered in connection with the accompanying .drawing, and those features which are believed to be novel and patentable will be pointed out in the claims appended hereto.

In the drawing, Fig. 1 is an explanatory diagram representing the type of apparatus to which my invention is applicable; Fig.2 is a schematic and circuit diagram or the arrangement of Fig. 1 explaining the eilect of temperature changes and showing the transmitter in one of its extreme end positions; Fig. 3 is a circuit diagram illustrating the arrangement of Fig. 1, modified to electrically provide temperature compensation; Fig. 4 is a schematic diagram illustrating a modified form or receiver with which m invention may also be employed; Fig. 5 represents a modification of the arrangement 01 Fig. 3 with an electrical temperature compensation system. Like reference characters are utilized throughout the drawing to designate like parts.

In Fig. 1, I'have illustrated a telemetering system comprising a transmitter ii and a receiver II with a direct current source of energy which may take the form of a battery It. The transmitter ll comprises a potentiometer resistor H with end terminals II and it, a movable brush or tap l'l adapted to slide along-the resistor 14 in response to variations in an indication or a meter reading to be transmitted to a remote point at which the receiver I2 is located. The brush l1 may be connected directly to one 01' the terminals, for example, thenegative terminal ii of the current source.

grounded. In the latter case the terminal It 01 u or, n desired, may be connection between the Patent No. 2,248,616,

' quently,

' a row ti.

. which is positive.

the current source iii is also grounded, and the brush ill and the battery terminal it takes place through the ire of the ship, vehicle or machine on which the telemetering sysmm is used.

The receiver l2 in the form illustrated in Fig. 1 comprises a pivoted rotatable magnetic element is and a stationary member or field structure comprising a pair of! angularly displaced electrical coils 26 and 26 with a core structure shown in the form of an annular or hollow cylindrical shield 22. The stator core and shield 22 may be composed of a suitable high permeability low hysteresis magnetic material, such as an alloy composed of approximately 78 per cent nickel and the remainder iron.

The movable magnetic element iii or rotor may be in the shape of a right circular cylinder pivoted around its cylindrical axis and composed of high coercive force permanent magnet material magnetized along a diameter of the cylinder. Such rotors do not constitute.my invention and a suitable form thereof is described in Fans. The rotor it may carry a pointer 28 cooperating with a graduated scale 26.

The stator coils 2d and iii are wound from insulated wire composed oi a suitable conducting material such as copper and are mounted as shown at an angle to each other within the shield 22, for example, about 120 degrees apart with their magnetic axes radial, and with the connections such that both coils cause radial magnetic fields of the same polarity to flow toward the center of the circle defined by the shield 22. the coil 2d tends to deflect the rotor it to the position with its line of magnetization toward the coil 20 and current flowing only in the coil 2i tends to deflect the rotor 89 to the angular position in which its line oi magnetization is toward the coil 26. nected through conductors 2t) and 2G, to the end terminals 95 and it; oi the transmitter poten tiometer it. The coils also have a Junction terminal it connected through a conductor 2%; to the remaining terminal, in this case the positive terminal 29 of the current source it.

Movement of the brush ill back and forth along the resistor it causes fractional rotation of the receiver rotor i9 and therefore deflection of the pointer 23 back and forth along the scale 26. This results from the fact that movement 01 the brush Ill varies the proportions oi? resistance of the potentiometer resistor i l in the circuits of the coils 2t and ti and therefore varies the relative currents in these coils. When The coils Eli and El are con-- iii asserts cordance with the usual practice the transmitter resistor is is composed of resistance material such as Constantin having a relatively low or zero temperature coefficient of resistance. With the elements in the position shown in Fig. 2,-when the ambient temperature rises the resistance of the coil it rises appreciably causing the current therein to fall. A proportionate rise in resistance of the coil 2i does not take place, however, for the reason that the circuit of this coilincludes the constantin resistor E6. The strength of the'magnetic field of the coil therefore weakens in proportion to the strength of the magnetic field of the coil 29 and the moyable element of the receiver i2 deflects toward the mid position, for example toward the position 23 along the dotted line 32. This large as 2 /2 per cent in the temperature variation of plus or minus 60 degrees from. a normal ainblent temperature of 10 C. Although I have used the expression copper wire coils" in the description and claims, it will be understood that my invention is not limited to the use of copper and the expression copper wire" isinwith its pointer variation may be as case of an ambient tended to include copper and equivalent materials. v

For overcoming this temperature error I provide an arrangement which reacts upon the movable magnetic element tive force toward the midscale position 33. The

Accordingly current flowing only in p Bit compensating arrangement is such that its effect becomes stronger. with fall in temperature and weaker with rise in temperature, thus counteracting the previously described effect of temperature variation on the relative strengths of the coilsiii and El which cause the movable element to deflect toward the mid scale position with a rise in temperature. The compensation arrangement in the case of a movable magnetic rotor is one which reacts magnetically with the rotor but may be in the form of either a mag netic element, as in the patent application, or electric elements acting inductively or as electiomagnets.

An exampleof an electrical arrangement for compensating the receiver id for temperature variations is illustrated in Fig. 3. The arrangement of Fig. 3 is particularly useful for overcom mg salt-heating errors of the coils 2t and 2%. 1h

this case the coils 2t and 2E are intimately associated thermally with a pair of bucking coils t5 and 36. For example, the coils 2i! and 28 may be the brush H is moved to one extreme position,

for example the left-hand end position asillustrated in Fig. 2, the coil 29 is connected directly across the current source it and the coil 2i is connected to the 'cur source in series with the resistance of the transmitter iii. Consea strong magnetic field 'is produced by the coil 2d represented by the heavy arrow to and a comparatively weak gnetic field is produced by the coil 2!! represented by the light The rotor it takes up position with its line of magnetization along the resultant of the magnetic flelds,--for example along the position in which the pointer 28 is represented.

The coils 2d and 29 are composed of copper or appreciable temperature coefiicient oi resistance the other hand, in acoverwound. with the latter coils are so connected that the currents therein act in opposition to the currents in the coils around which they are wound. Furthermore, the bucking coils 35 and 36 are each connected in circuit with the opposite main coil of the receiver; that is, the bucking coil 35 is in circuit with the @main coil 2| and the bucking coil 88 is in circuit with the main coil 20. The coils 35 and 36 may be connected to the coils 20 and 2t in a bridge arrangement. Thus the coils 35 and 35 may have a junction terminal connected in series with a resistor 38 to the transmitter brush i'l, so that the coil 36 is in series with'the coil 2d between the junction terminals 27 and 31 and the coil 85 is in series with the coil 25 between the Junction terminals 2? and 37.

It will be appreciated that serious self-heating error can occur in case the transmitter brush has been in one position for a long period of time and is suddenly shifted to a much ,difierent position. For example, if the transmitter brush ll has been it setting up an attracbucking coils 35 and 86. The

at the left-hand position represented by Fig. 2 the greater current has been flowing through the main receiver coil 20 causing it to be more greatly heated. Then, if the transmitter brush i1 is shifted to the opposite end of the transmitter resistor II the greater. voltage is applied to the other main receiver coil 2| which is then considerably cooler than-the coil 20. Consequently the coil 2| has abnormally low resistance in comparison with the coil -20 and an abnormally high current flows through it in comparison with the coil 25. This causes the pointer 23 to take up a position at flrstwhich is too far away from mid scale and then to drift toward the mid scale position. In order to overcomethis self-heating error and the pointer drift, the arrangement of Fig. 3 may be provided in which each coil has a bucking element in thermal relation to the opposite coil. Thus the self-heating effect of the coil 2|], for example, which would cause it t be too weak, is overcome by the fact that self-heating of the coil results also in heating of the bucking coil 85. The weakening of the bucking coil results in overcoming the self-heating effect of the main coil 2.. As the transmitter brush I1. is moved to the varied.

It is not necessary that the coils 35 and 35 be inductive. I have found that still greater compensation of the self-heating error of the main coils 20 and 2| may be accomplished by making thecoils 35 and ,36 simple resistance units without inductive effect but in thermal relation to the instrument coils such that the coil heats the V resistance element and vice versa. The same I rent from the coil 20 so as to bring about some compensation of the self-heating error.

While I have described my temperature compensating arrangement in connection with a receiver of the type having coils with radial magnetic-axes as illustrated in Fig. 1, it will be understood that my invention is not limited to the use with instruments or receiver's of this specific type of construction. It may also be employed with receivers of the type illustrated in Fig. 4 having a broken toroidal core 22' with coils 20' and 2i which link the core 22' and having magnetic axes circumferential with respect to the core 22'. In this case each of the coils 20' and 2i tends to deflect the rotor l9 to the position in which the pointer 23 is away from the coil having the greater current. However, the weakening of either coil by increase of its resistance with rise in temperature tends to cause the pointer 23 to deflect toward mid scale just as in the arrangement in Fig. l. I

The same type of compensation may therefore be employed and windings corresponding toll and 36 of Fig. 3. or noninductive elements corresponding to 35' and 38' of Fig. 5 will be asumed to be included in the integral winding structure illustrated in Fig; 4. The inner connections to the winding structure of Fig. 4 represent the connection of such compensating coils or elements,

- the connection thereof being in accordance with Fig. 5. The telemetering circuit and general re out temperature compensation) is not my invention but is described in connection with Fig. 3 on page 5, lines 29 et seq. of the copending application of Robert G. Ballard, Serial No. 424,779. filed December 29, 1941, and assigned to the same assignee as the present application.

Although in Fig. 3 I have described a specific arrangement for overcoming self-heating errors in which coils are provided in circuit with one main coil and heated in response to heating of the opposite main coil, it will be understood that my invention is not limited to that specific arrangement.

Another arrangement for overcoming self-heating errors is illustrated in Fig. 5. In this case the main coils in and ii are overwound or inv timately thermally associated with elements 35' and 38' which are noninductive, or which are so arranged as to have no magnetic effect on the rotor i9. They functionsimply as resistors subjected to the heating effects of. the coils ll and ii. In the arrangement of Fig. 5 the resistor 35' is connected directly in series with the opposite receiver coil II to the transmitter terminal l6. Likewise the resistor 38' is directly connected in series with the opposite receiver coil 20 to the transmitter terminal l5. e resistors 35' and 85' are so proportioned preferably that the total variation in resistance of the resistor is the same for given temperature rise as that of a receiver coil and the heating produced by a given current flow is the same as that of a receiver coil. Thus, the temperature effect is mutual. The flow of current of a given value through the resistor 35' produces a given temperature rise in the receiver coil 20 and vice versa. Although the arrangement of Fig. 5 produces er:- tra heating loss it produces constant and. equal total self-heating eflects in the coils 20 and 26. As the current in one of the receiver coils fails oil tending to reduce its self-heating the current in the accompanying resistor rises proportionately tending to increase the self-heating to the original value. Accordingly self-heating of the coils is compensated in the arrangement of Fig. 5.

I have herein shown and particularly described certain embodiments of my invention and certain methods of operation embraced therein for the purpose of explaining its practice and showing its application, but it will be obvious to those skilled in the art that many modifications and variations are possible and I aim therefore to cover all such modifications and variations as fall within the scope of my invention which are defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A receiver for a direct current telemetering system in which indications are produced by varying the relative proportions of low-temperature coefllcient resistance in two circuits, said receiver comprising a pair of copper-wire coils angularly disposed, a movable magnetic element in inductive relation to said coils adapted to defleet in response to variations in ratio of currents in said coils. and a self-heating compensation circuit comprising a pair of bucking coils each mounted with one of said first-mentioned pair of coils but wound to act in opposition thereto and connected in series with the opposite coil of the first pair in a bridge circuit, whereby temperature difference between coils of the first pair due to greater self-heating oi. one is compensated by opposite temperature difference of the buckin: coils. j

2. A receiver for a telemeterin'g system in which indications are produced by varying the relative proportions of low-temperature coemcient of resistance in two circuits, said receiver comprising a pair of copper-wire coils angularly disposed, a movable magnetic element in inducvarying the relative proportions oi low temperature coeflicient resistance in two circuits, said receiver comprising a pair of copper wire coils angularly disposed, a movable magnetic element in inductive relation to said coils'adapted to deflect in response to variations in ratio of currents in said coils and a self-heating compensation circuit comprising a pair of resistance elements each having an appreciable temperature coefllcient of resistance and each being mounted with one of said first-mentioned pairs of coils in thermal relation thereto and connected in series with the opposite coil in a bridge circuit whereby temperature diflerences between the coils due to greater self-heating of one is compensated by opposite temperature diflerence andvariation of resistance in the compensating elements.

FREDERICK R. SIAS. 

